This invention is an improvement in methods and equipment for installing small diameter columns of granular material in soil, including installation of granular drains, which permits column formation in soil without the loss of time related to interruption of the production cycle to supply granular material used to form the columns in soil. The equipment for column installation is configured to minimize weight applied to the hollow shaft cavity forming element or tool, termed “mandrel”, as compared to other apparatus applicable to the installation of small diameter columns of granular material in soil.